Dose Volume Constraints for Organs at Risk

Dose Volume Constraints for OARs
Conventional fractionation

Spinal Cord – 40 Gy (max)

Brainstem – 54 Gy (max)

Optic nerves – 54 Gy (max)

Parotid Glands – 35 Gy (max)
25 Gy (<50%)

Brain – 50 Gy (minimize volume above 30 Gy as much as possible)

Mandible – 70 Gy (max)

Cochlea/Middle Ear – 30 Gy (max)

Oral Cavity – 30 Gy (mean)

Brachial Plexus – 60 Gy (max)

Posterior Neck Avoidance – 45 Gy (mean)

Lens – 5 Gy (max)

Eyes – 45 Gy (max)

Optic Chiasm – 54 Gy (max)

Optice Nerves – 54 Gy (max)

Lung – 20 Gy (<35%)

Heart – 40 Gy (max)

Esophogus – 60 Gy (<50%)

Kidney – 20 Gy (max)
< 50% of combined both kidneys
< 75% of one side of kidney if another kidney is not functional

Liver – 30 Gy (<40%)

Femoral heads – 45 Gy (max)

Small Bowel – 48 Gy (max)

Rectum –
40 Gy (<60%)
45 Gy (<50%)
60 Gy (<40%)
70 Gy (<20%)
75.6 Gy (<15%)
78 Gy (<5%)

Bladder – 70 Gy (<20%)

Femoral Heads – 45 Gy (<50%)

Pituitary gland – 36 Gy (max, adults), 18 Gy (max, children), very safe


Dose Volume Constraints for OARs
SRS, single fraction
Brainstem – 12 Gy (max)
Optic nerves – 12 Gy (max)
Optic Chiasm – 12 Gy (max)
Optice Nerves – 12 Gy (max)
Retina – 12 Gy (max)
Normal Brain – 20 Gy (max)
Lens – 2 Gy (max)
Skin – 5 Gy (max)


Dose Volume Constraints for OARs
SBRT, 3-5 fractions

Spinal Cord – 18 Gy (max), 10 Gy (<10%) single fraction
3 Gy per fraction always safe, only draw cord within 4 mm of PTV

Lung – 20 Gy (<15% of total lung capacity) total

Heart – 6-8 Gy (max) per fraction

Esophogus – 6 Gy (max), 4 Gy (<75%) per fraction

Stomach – 8 Gy (max) per fraction

Small bowel – 4 Gy (max) per fraction

Kidney – 1 functioning kidney: 2 Gy (max), 1 Gy (<75%) per fraction
2 kidneys: 3 Gy (max) per fraction to one, test to make sure both work

Liver – 15 Gy (<700 cc) total

Bronchii and trachea – 8 Gy (max) per fraction

Skin – 4 Gy (max) per fraction

Mayneord F Factor

Mayneord Factor
* Overestimates the increase in PDD with increase in SSD
* Overestimates for small field sizes
* MF = ((f2+ dm) /(f1 + dm))squared x ((f1 + d) / (f2+ d))2

PDD (Percentage Depth Dose) Key Points.

PDD

Increases with FS (less dependent with higher E)
Increases with E
Increases with SSD (due to ISL)
Decreases with Depth (exponentially) beyond build up region

FILM: EDR VS XV

The two films are different in their response to dose:
XV films being to saturate at about 30 cGy
EDR2 films begin to saturate at about 300 cGy

The difference between the two films originates from their differences in the content of silver bromide crystals and grain size.

The grain size of EDR2 is smaller.

DOSIMETRIC PERFORMANCE
Compared with XV film, EDR2 film showed better agreement with calculations and measurements of dose. (olch2002)

EDR 2 film is less sensitive to low energy photons.

XV requires less amount of dose and thus the irradiation will be much quicker. On the other hand it will saturate much quicker than EDR2 film.

Source Film dosimetry (Yeo and Kim)